[G4] G4 MDD won't wake up

[Harold Polk]

I have a G4 MDD that has trouble waking up after going to sleep  
either time out or manual.  However, if I only let the display go to  
sleep, 20 minutes, and keep the computer running, preference set to  
"never," it works fine, the display wakes up every time.
I have done the following:

1. all the maintenance procedures, daily, weekly and monthly. cleaned  
the caches.
2. zapped the pram
3. reset the PMU
4. removed the battery and left it out for over 30 minutes. then  
replaced the battery, and reset the PMU.  Battery voltage is 3.6 volts.
5. replaced the graphics card with one that is known to work.

No additional PCI cards.
The memory sticks are the original 245megs from Apple
3- 512 megs Kingston sticks
All memory seems to check out with the memory checkers.
I do occasional get kernal panics.

The problem presists.
Any ideas would be appreciated.

Harold